1. Field of the Invention
The present invention relates to a plating apparatus for a substrate, and more particularly to a plating apparatus for a substrate used for filling a fine interconnect pattern formed in a semiconductor substrate with metal (interconnect material), such as copper, so as to form interconnects.
2. Description of the Related Art
Recently, there has been employed a circuit forming method comprising forming fine recesses for interconnects, such as interconnect trenches or via holes in a circuit form, in a semiconductor substrate, embedding the fine recesses with copper (interconnect material) by copper plating, and removing a copper layer (plated film) at portions other than the fine recesses by means of CMP or the like.
A plating apparatus having the following configuration has been known as this type of plating apparatus used for plating to form fine interconnects having high aspect ratios. A substrate is held in such a state that a surface (surface to be plated) of the substrate faces upward (in a face-up manner). A cathode electrode is brought into contact with a peripheral portion of the substrate so that the surface of the substrate serves as a cathode. An anode is disposed above the substrate. While a space between the substrate and the anode is filled with a plating solution, a plating voltage is applied between the substrate (cathode) and the anode to plate a surface (surface to be plated) of a substrate (for example, see Japanese laid-open patent publication No. 2002-506489).
In a plating apparatus in which a substrate is held and plated in single wafer processing while a surface of the substrate faces upward, a distribution of a plating current can be made more uniform over an entire surface of the substrate to improve uniformity of a plated film over the surface of the substrate. Generally, the substrate is transferred and subjected to various processes in such a state that a surface of the substrate faces upward. Accordingly, it is not necessary to turn the substrate at the time of plating.
Meanwhile, in order to deposit a copper plated film selectively in interconnect trenches in a circuit form or the like, there has been known a method of bringing a porous member into contact with a substrate such as a semiconductor wafer, and plating the substrate while relatively moving the porous member in a contact direction. As a porous member in this method, there have generally been used PVA, porous Teflon (registered trademark), polypropylene knitted like a textile or skimmed like a paper, and unformed materials such as gelated silicon oxide or agar (for example, see Japanese laid-open patent publication No. 2000-232078).
However, in a method comprising bringing a porous member into contact with a substrate and plating the substrate while relatively moving the porous member in a contact direction, it is difficult to uniformly press the overall surface of the porous member against the surface, to be plated, of the substrate so as to bring it into close contact with the surface of the substrate because of the surface roughness of the surface of the porous member or a pressing member for pressing the porous member against the surface to be plated, or undulations or warpages produced in the porous member when the porous member is pressed against the surface, to be plated, of the substrate. For this reason, gaps are locally formed between a porous member and a surface, to be plated, of a substrate. Thus, plating non-uniformity is caused over the surface of the substrate.
It is considered that the entire surface of the porous member can be brought into contact with the surface, to be plated, of the substrate closely by increasing loads to bring the porous member into contact with the substrate to be plated. In such a case, an extremely large load is applied to the substrate. Accordingly, in a case where a soft interlevel dielectric layer such as a low-k material is processed, the interlevel dielectric layer is broken, and a surface of a plated film is likely to be scratched. Thus, it has been difficult to put the above method into practice. Even if the entire surface of the porous member can be brought into contact with the surface to be plated under a high load applied thereto, the pressure under which the porous member and the surface to be plated tends to vary from place to place, causing the porous member and the pressing member which presses the porous member against the surface to be plated to transfer their surface irregularities, undulations, and warpages directly to the plated film.